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node_modules/rxjs/operators/reduce.js

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+"use strict";
+var scan_1 = require('./scan');
+var takeLast_1 = require('./takeLast');
+var defaultIfEmpty_1 = require('./defaultIfEmpty');
+var pipe_1 = require('../util/pipe');
+/* tslint:enable:max-line-length */
+/**
+ * Applies an accumulator function over the source Observable, and returns the
+ * accumulated result when the source completes, given an optional seed value.
+ *
+ * <span class="informal">Combines together all values emitted on the source,
+ * using an accumulator function that knows how to join a new source value into
+ * the accumulation from the past.</span>
+ *
+ * <img src="./img/reduce.png" width="100%">
+ *
+ * Like
+ * [Array.prototype.reduce()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/reduce),
+ * `reduce` applies an `accumulator` function against an accumulation and each
+ * value of the source Observable (from the past) to reduce it to a single
+ * value, emitted on the output Observable. Note that `reduce` will only emit
+ * one value, only when the source Observable completes. It is equivalent to
+ * applying operator {@link scan} followed by operator {@link last}.
+ *
+ * Returns an Observable that applies a specified `accumulator` function to each
+ * item emitted by the source Observable. If a `seed` value is specified, then
+ * that value will be used as the initial value for the accumulator. If no seed
+ * value is specified, the first item of the source is used as the seed.
+ *
+ * @example <caption>Count the number of click events that happened in 5 seconds</caption>
+ * var clicksInFiveSeconds = Rx.Observable.fromEvent(document, 'click')
+ *   .takeUntil(Rx.Observable.interval(5000));
+ * var ones = clicksInFiveSeconds.mapTo(1);
+ * var seed = 0;
+ * var count = ones.reduce((acc, one) => acc + one, seed);
+ * count.subscribe(x => console.log(x));
+ *
+ * @see {@link count}
+ * @see {@link expand}
+ * @see {@link mergeScan}
+ * @see {@link scan}
+ *
+ * @param {function(acc: R, value: T, index: number): R} accumulator The accumulator function
+ * called on each source value.
+ * @param {R} [seed] The initial accumulation value.
+ * @return {Observable<R>} An Observable that emits a single value that is the
+ * result of accumulating the values emitted by the source Observable.
+ * @method reduce
+ * @owner Observable
+ */
+function reduce(accumulator, seed) {
+    // providing a seed of `undefined` *should* be valid and trigger
+    // hasSeed! so don't use `seed !== undefined` checks!
+    // For this reason, we have to check it here at the original call site
+    // otherwise inside Operator/Subscriber we won't know if `undefined`
+    // means they didn't provide anything or if they literally provided `undefined`
+    if (arguments.length >= 2) {
+        return function reduceOperatorFunctionWithSeed(source) {
+            return pipe_1.pipe(scan_1.scan(accumulator, seed), takeLast_1.takeLast(1), defaultIfEmpty_1.defaultIfEmpty(seed))(source);
+        };
+    }
+    return function reduceOperatorFunction(source) {
+        return pipe_1.pipe(scan_1.scan(function (acc, value, index) {
+            return accumulator(acc, value, index + 1);
+        }), takeLast_1.takeLast(1))(source);
+    };
+}
+exports.reduce = reduce;
+//# sourceMappingURL=reduce.js.map